What is the reason for the idle speed not increasing when the air conditioner is turned on?
4 Answers
The reasons and functions for the idle speed not increasing after turning on the air conditioner are as follows: 1. Reasons: (1) Poor performance of spark plugs; (2) Vacuum tube leakage; (3) Malfunction of the idle control valve; (4) Faulty throttle position sensor; (5) Idle step motor failure; (6) Air intake system leakage. 2. Functions of the air conditioner: (1) Achieving cooling effect through the continuous cycle of refrigerant; (2) Removing dust, odors, smoke, and toxic gases from the air inside the car, making the air fresher, humidifying the air inside the car, and increasing the relative humidity of the air inside the car.
Last time my car's AC was on but the idle didn't respond. I thought about the common causes: it might be that the idle control valve is stuck. The engine should automatically increase RPM to compensate for the AC load, but carbon deposits or dirt may be blocking its response. Or there could be an issue with the compressor circuit, where the fan isn't running at full capacity, affecting the engine load. ECU sensor signal failures are also common, such as misreading the throttle position. I've noticed that when the battery ages, voltage instability can cause these systems to fail. It's recommended to first check if the AC fuse in the fuse box is blown—try a simple replacement. If that doesn't work, go directly to a repair shop to scan for ECU error codes. Don't delay too long to avoid causing stalling issues.
I always think the idle system is delicate work. When the AC is turned on, the RPM should increase but doesn't, mostly due to issues in the idle control circuit. When engine load increases, the idle speed motor needs to receive ECU commands to act quickly. However, if sensors like the intake pressure or temperature send wrong signals, the ECU misjudges. Poor contact in the compressor clutch or a loose belt, resulting in insufficient load increase, could also be the cause. I often remind friends to use a diagnostic tool to check for error codes, and to clean valve port carbon deposits or check for loose wiring connections themselves. Regular maintenance can greatly reduce such problems, especially when the AC is used frequently in summer.
Common causes of idle speed not increasing: Air conditioning compressor malfunction not starting the load; Idle speed motor stuck or slow to respond; ECU receiving incorrect signals; Or low battery voltage causing system sluggishness. Address promptly to avoid engine stalling hazards.
